1. Field of the Invention
The present invention relates to a high voltage semiconductor device such as a gate turn-off thyristor or the like and a method of fabricating the same, and more particularly, it relates to withstand voltage increase and capacity enlargement thereof.
2. Discussion of the Background
It is known that avalanche breakdown takes place at a voltage lower than a withstand voltage of original real ability of a P-N junction in a high voltage semiconductor device such as a high voltage diode or a high voltage gate turn-off thyristor and the high voltage semiconductor device cannot be fabricated unless a surface field of a main P-N junction is weakened.
Therefore, a technique called bevel formation for weakening the electric field by inclining an exposed part of the P-N junction is known.
However, there has been such a problem that, although a device thus inclined, i.e., bevelled, can attain withstand voltage increase as compared with a device not subjected to the bevelling, chipping readily takes place in an edge part formed on a boundary part between its outer peripheral part and the said bevelled part in fabrication, field concentration results from a strain field generated in the chipping part, withstand voltage increase is inhibited, and stable provision of a semiconductor device of a high withstand voltage is difficult as a result.
Particularly as to chipping, there has been such a problem that its influence is large in a semiconductor device of a large capacity in which the diameter of a semiconductor element is large, i.e., the outer peripheral length of the semiconductor element is long, and stable provision of a semiconductor device of a high withstand voltage and a large capacity is difficult as a result.